dependence ring compile error in mips64 platform

[RickSKy]

error: failed to run custom build command for `ring v0.16.20`

Caused by:
  process didn't exit successfully: `/home/ub/target/release/build/ring-c17fa5ea40a1072c/build-script-build` (exit status: 101)
  --- stderr
  thread 'main' panicked at 'called `Option::unwrap()` on a `None` value', /home/test/.cargo/registry/src/github.com-1ecc6299db9ec823/ring-0.16.20/build.rs:358:10
  note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace
warning: build failed, waiting for other jobs to finish...

maybe optional openssl or ring will be bettre for more platform

[est31]

Thanks for the feedback. For the upstream issue of ring not compiling, see briansmith/ring#562 .

For the question of whether we should make ring optional or not, see #74 .

I'm closing this in favour of the two issues.